Corduroy velvet textile articles are well known and widely spread in the field of apparel and garments. Corduroy is made, as will be familiar to the man skilled in the art, by preparing a base fabric having lengthwise rows (or ribs) of weft yarn loops protruding upward from the general plane of the base fabric and thus forming lengthwise channels on the fabric. In a separate step, these channels are opened by leading the fabric over a generally flat and horizontal bar, and introducing needle-like cutters into said loop channels, one cutter needle in each channel. When advancing the textile web against these needles and relative shaft--which are arranged in side-by-side relationship over the horizontal bar--the loops are cut and the corduroy velvet is formed. The advancing speed of the web is about from 10 to 20 m/min, typically about 12 m/min.
It occurs rather frequently that a cutting needle pierces the fabric, i.e. it makes a downside exit, or goes upward or sideways out of the respective loop channel, i.e. it makes an upside exit. This occurs since the needles can only be guided at their rear, non-cutting end, and the fabric to be treated is not perfectly homogeneous. In this case, where a needle leaves the channel where it is working, be it downside or upside the channel, the fabric advance must be stopped, and the needle out of order must be located, and properly reinserted into the channel.
Although reinsertion of the needle is a very rapid operation, it is very troublesome to find the needle that is out of order, and it is nearly impossible to detect a defective state of one or more needles when the machine is running and the web is normally advancing.
Electromechanical devices have been proposed to detect outcoming cutting needles. It is easy to detect even one downside outcoming needle, since such a needle is pushed against the metallic bar over which the fabric web is guided for cutting by the very movement of the web, and thereby establishes a fairly good electrical contact. However, upside outcoming needles could hitherto only be detected by electrical contact with a metallic bar placed over the fabric, but this technique is not reliable enough. Detection by the human eye is impractical, rapidly wearing down the physical condition of the supervisor. It must be realized that the number of parallel needles arranged in a needle bed is normally between 600 and 1000. Furthermore, even if the inspecting person, by chance, rapidly detects a needle coming out upside of a loop channel, some time elapses until the machine can be stopped.
It need not be emphasized that a needle coming outside a loop channel will result in faults in the textile material. These faults, namely uncut rows in the produced corduroy, are immediately visible and depreciate the product.
One could imagine the installation of a measuring system over the needle bed and the support bar where loop cutting is performed, based upon changes in capacitance or inductance. However, tests and experiments which have been made show that these systems would not give signals which are sufficiently distinct and characteristic for detecting an emerging needle.
Therefore, there is a need for an apparatus which can rapidly detect needles coming out of a loop row on the upper side of a corduroy fabric web during a cutting operation, regardless of whether the needles emerge at the top or at side locations of the row.